Electrolytic condenser



Aug. 27, 1935. J PQITRAS 2,012,691

ELECTROLYTIC CoNDENsE' Filed March 26, 1934 I 1 g L5 INVENTOR JUSEPHAPOIT AS A I 4 f ATTORNEY6 Patented Aug. 27, 1935 PATENT OFFICEELECTROLYTIC CONDENSER Joseph A. Poltrar, Fort Lee, N. 1-. asalgnor toSolar Manufacturing Corporation, a corporation of New York ApplicationMarch as. 1934,8erial No. 111,347

,8 Claims.

My invention relates to electrolytic devices, such as electrolyticcondensers, rectifiers or the like, comprising film-forming electrodes.These condensers are based upon the well known prin- 5 ciple that whencertain metals, as for instance aluminum, tantalum, etc. are used aselectrodes and are placed in suitable electrolytes, they are uponapplication of the proper voltage covered by a film which, as far asconductivity is concerned, is of a uni-directional character.. Thesecondensers are used for different purposes, one of their uses being infilter circuits to eliminate the alternating current ripples fromrectified currents. However, it should be well understood that myinvention is not limited to such purposes and applications.

, when electrolytic condensers are used for the above stated purpose,only one of the electrodes, namely, the anode, is required to be offilm-forming metal,preferably aluminum. The cathode which, as a rulealso forms the container of the condenser, is usually made of a metalwhich does not exhibit film-formation, or at least, not to a markedextent, as such film-formation on the cathode always results in asmaller initial capacity and larger power factor than desirable.However, in practice it has been found that for economical reasons, inspite of this drawback, containers of aluminum which serve as cathodesare quite practical, and their shortcomings in the above mentionedrespect may be overcome by diffel'ent means, one of which is, amongother advantages, embodied in the improved novel construction, about tobe described. Aluminum can be easier subjected to mechanical operations,and electrolytic condensers with an aluminum container, serving ascathode, are far less expensive, and also much lighter than those madewith a copper or nickel cathode.

Aside from this incidental feature, i. e., the improved serviceabilityof an aluminum cathode container, the special improvement and novelfeatures which characterize this invention, are however not concernedwith the formation of the aluminum (or any other metal) cathode but withthat of the aluminum anode, and moreover they are confined to only. onespecies of electrolytic condensers, namely so-called spiral-woundcondensers. The general principle, on which these condensers are built,is as follows: The anode, composed of aluminum or other metal, capableof forming the necessary dielectric film on its surface, is a strip ofsheet metal fastened to and wound spirally around a stiff rod of thesame metal. This rod'usually forms the anode terminal. The turns arespaced apart by different means, usually depending only upon theirresiliency and tendency to spread, analogous to the way a watch springwould spread. Sometimes the sheets were perforated by apertures whose(Cl. 17H

punched out, extruded or burred edges served as eventual spacers betweenadjacent turns. No special insulating layers or separators were thoughtnecessary, neither between the turns of the spirally wound sheet norbetween the whole anode coil and the'cathode wall, as the dielectricfilm of aluminum oxide, formed all over the anode sheet, was supposed tosufiiciently insulate adjacent elements from each other. Sometimes acelluloid or cellophane sheet was inserted between the container walland the anode element. This arrangement has proved in practice deficientin different and opposite directions. A nearly impervious insulatingsheet, like cellophane or celluloid, ofiers too much resistance to thedesirable free circulation of the electrolyte solution; on the otherhand, if one depends upon the insulating quality of the oxide filmalone, it will in the long run not be found very reliable. By accidentalcontact the film layer is easily rubbed off in places, and ashort-circuit path is formed without a chance of repairing the brokenfilm. This changes the surface capacity and the power factordetrimentally, if the short circuit is confined to the turns of theanode alone, but if the inner container surface and the outer peripheralturn of the anode element is short-circuited, the condenser is rendereduseless. But even if no actual metallic contact occurs between the outerturn of the anode electrode and the inner surface of the container,unprotected by either an insulating sheet or by plating with anothernonfilming metal, the aluminum cathode is still liable to quicklydeteriorate or corrode. One reason is that when the condenser is used,the alternating current ripples, passing through the condenser, if ofsumcient magnitude, have the tendency to gradually build up a film onthe cathode too, through electrolytic action of the current fiowing atminute intervals in a direction opposed to that of the direct currentcomponent of the rectified current. The same thing results from theself-induced countercurrent which occurs whenever the source of currentis being switched off. And this film-forming action is advanced by theabsence of any impediments in the path of the ionic components. The filmthus formed on the cathode represents a capacity which is in series withthe capacity of the film on the anode and this series combination of thetwo capacities reduces the efilciency of the condenser. However, as longas the voltage of the ripples is small, compared with the voltage of thedirect current component, the film formation, due to this cause, wouldnot be sufficient to explain the great drop of efliciency whichnevertheless often occurs and is accompanied with a considerableoxidation and even corrosion of the inside of the container, and we willhave to look for a further cause for this phenomenon.

It is known that due to electrolytic action during operation, oxygen isliberated from the electrolytic solution, which partly escapes, but isalso liable to attack the cathode,especially during the intervals when aripple occurs and the polarity is momentarily reversed-by purelychemical action. The oxide film thus formed through purely chemicalaction of the oxygen is similar to that effected by electrolytic action,but the power factor of such chemically built-up film is much larger(about 100%) than that of an electrolytically formed film of the samethickness, as experiments have proven. This deleterious effect is themore noticeable the nearer the outer anode surface is to the cathodecontainer, and the less impediments there are to prevent an accumulationof gas bubbles on the latter. To eliminate these different drawbacksmentioned is the general purpose of the present invention.

It is therefore among the objects of this invention to provide meanswhereby a metallic contact between the inner turns of a spirally-woundanode sheet of an electrolytic condenser is effectively prevented.

Another object of this invention is to provide means whereby a metalliccontact with consequent short-circuit between the outer turn of theanode-spiral and the cathode, representing the container of theelectrolyte, is prevented.

A further object of this invention is to provide insulating meansbetween the separate turns of a spirally-wound condenser or between theoutside surface of the anode spiral and the cathode container which donot interfere with the free circulation of the electrolytic liquid.

A further object of my invention is to provide insulating means, servingthe aforesaid purposes which are adapted to intercept the gas bubblesformed during electrolytic action and prevent their accumulation on thecathode electrode.

Another object of my invention is to arrange the insulating means insuch a way that sparking over or loss of capacity by so-calledcoronaeifect between the extreme edges of the anode spiral and thecathode container is minimized.

Another object of my invention is to provide such construction of theanode electrode, that free circulation of the electrolytic solution isfacilitated.

This circulation, if it were to follow its natural course in anunobstructed cylindrical container with a liquid electrolyte would forman ascendlng central column of warmer liquor, spreading out radiallynear the top in mushroom-like fashion and returning toward the centernear the bottom.

Another object is to provide means whereby the free gas bubbles, formedduring electrolytic action, are more quickly deprived of their electriccharge and consequently will be discharged toward the surface in aneutral non-electric state.

A further object is to provide supporting means whereby the insulatinglayers provided between the spiral turns are securely kept in place andtheir dislocation is prevented.

Other more specific objects and advantages of my device will appear asthe nature of the improvements is better understood, the inventionconsisting substantially in the novel arrangement and correlation ofinstrumentalities herein fully described and illustrated in theaccompanying drawing wherein similar reference characters are used todescribe corresponding parts throughout the several views and thenfinally pointed out andspeciflcally defined and indicated in theappended claims.

The disclosure made the basis of exemplifying the present inventiveconcept suggests a practical embodiment thereof, but the invention isnot to be restricted to the exact details of this disclosure, and thelatter therefore is to be under stood from an illustrative, rather thana restrictive standpoint. It will be also understood that the variousfeatures of the present invention disclosed may be separately applicabledespite their cooperation herein shown.

In the accompanying drawing Fig. 1 is a sectional elevation of anelectrolytic condenser, embodying the principles of my invention,showing the anode electrode partly in full. The section is taken alongline l| of Fig. 2.

Fig. 2 is a horizontal cross section through such a condenser,illustrating the manner in which the anode is wound.

Fig. 3 is a similar horizontal cross section illustrating a modificationof the winding.

Fig. 4 is a top view, partly sectional of the condenser, showing theventing device.

Fig. 5 is a fragmental sectional view, showing a modification of theventing device.

Fig. 6 shows the terminal connection for the anode electrode.

Fig. 7 is a detail showing how the insulating gauze may be held in placeby a corner clip of the aluminum sheet as at A, Fig. 2.

Fig. 8 is a detail showing how the end of a gauze strip may be clippedto the continuous edge of an aluminum sheet, as at B, Fig. 3.

imilar characters denote similar throughout the different views.

Referring more in detail to the separate views, the container 20 formsthe anode electrode and,

parts as already said, may be of aluminum, although it could be made ofa non-fllm-forming, non-corrosive metal, like copper or nickel. Theelectrolyte 2! is indicated as being liquid.

The outer container 20 can be shaped in different ways, but in themajority of cases it may be formed from a tubular blank, by contracting,pressing or spinning one end over a suitable mandrel into the properform. The tube is contracted by spinning to a smaller diameter and thendrawn out to a tubular neck 28. Over this neck the sleeve 29 is slippedand the protruding end 30 of the container neck is swaged out over theend of the sleeve by a spinning tool to retain the sleeve in place.Through this neck 28 protrudes the terminal 23 of the anode 22 whichwill bedescribed later, and the space between the tubular neck and theterminal is filled by an insulating substance 3|, like rosin or asphaltwhich hardens, when cooled.

Generally the terminal end of the condenser is supported on a bracket orplatform 32 in any suitable manner. If the outside of the sleeve isthreaded, a hexagonal nut 33 can be used to clamp the sleeve and therebythe condenser to the platform which is apertured in a suitable manner. Awasher 34 and a plate 35, adapted to serve as a binder post forattaching the cathode lead 36 to it, can be inserted around the sleeve29 where it passes through the aperture in the platform.

The upper end of the container is closed hermetically in the followingway: A dished or cupped end member is inserted into the open end of thetubular container 20. The outer flange 60a of this member has an inwardinclination so that the general shape of this cupped member resembles aconical frustrum, though only slightly deviating fromthe cylindricalform. The outer diameter of the bottom is equal to the inside diameterof the tubular member 20 and, after the cupped member 6. is inserted toits proper depth into the assembled container, the outer rim 2.1 of thecontainer is tightened by spinning it to ward the conical wall of thecupped member 82. At the same time theupper rim 60b is spun outwardlyand crimped over the contracted rim 221' so as to form a tightlyinterlocking Joint with the latter.

The middle portion of the cupped member ill is raised to form acylindrical head OI which has a central larger opening and one or moresmall perforations 62 through which gas under pressure can escape. Thegas holes are normally kept closed by a safety valve which may be ofvarious constructions, and is shown and described in the copendingapplication. Ser. No. 717,348, filed March 26, 1934, but for which nospecial patent protection is claimed here. These valves substantiallycomprise an annular soft rubber gasket 62 which covers the gas holes 62,a mushroomlike lid 64' which is clamped over said gasket, and asaddle-shaped clasp 65 which is resiliently clamped againstthe innerside of the raised head SI and coupled to the center of the lid by meansof a rivet il The resilient cushion of the clasp consists of msoftruhherring 61. When there is surplus gas pressure in the condenser, the gasket63 together with the lid 84 is raised against the resiliency of rubberring 61 to let the gas escape from under the gasket 63.

A modification of the venting device, which is likewise claimed andmore" fully described in said separate copending application, isshown inFig. 5. In this case the dished: end member 31 is recessed in the middleand spun inwardly to form a funnel-like nozzle 21a in which the ventholes 21b are provided. A rubber valve body 28 plugs up the centralfunnel mouth of the nozzle, and its fiared out upper flange 38aresiliently covers the vent holes 31b. The gas releasing function ofthis device is analogous to the one above described.

The novel and peculiar construction of the anode member 22 is now'to bedescribed.

As already said, it consists substantially of a film-forming aluminumsheet, rolled into a spiral. For the sake of cleamess only a smallnumber of convolutions is shown in Figures 1, 2, and 3, and also thethicknesses of the conducting as well as the insulating sheets are showngreatly exaggerated. It is to be understood that actually the condenserswill be of much smaller size and the spirals will be more closely wound.In order to facilitate the circulation of the electrolyte the aluminumsheet is perforated in any de sired way as shown at 40' in Fig. 6. Afurther improvement for the same purpose which also provides an easierascension of the gas bubbles in the axial zone of the condenser andthereby starts a tendency of the. warmer liquid to circulate by risingthrough the middle, and descending at the periphery, as the arrows inFig. 1 indicate, lies in the feature that, contrary to otherspiral-wound condensers, the solid rod to which the inner end of thealuminum is usually attached along its edge in flag-like fashion, isomitted in this construction. Only at the lower edge, as shown in Fig.6, a shortstub ll of the terminal 23 is fixedly attached to the anodesheet 22, by inserting the latter into a diametral slot of the terminal.Under the shoulder 24 an insulating washer ll is seated. Its mainfunction is to guard the anode element against any short circuit whichmay otherwise be gradually built up between the bottom of the containerand the lower edge of the spiral by sediments from electrolytic action.

The shank 42 of the terminal underneath the shoulder is tapered,principally to strengthen the hermetical sealing between the tubularneck 28 and the insulating sleeve 3i when the outer nut 44, threaded onthe reduced end I of the terminal 22, is tightened, also to prevent anupward dislocation of the insulating substance by frictional stressexerted by the shank 42, if the nut is loosened and the condenser may beturned upside down. A washer 45 is inserted between the nut 44 and theswaged over flange 30 of the neck 28.

To provide insulating means between the separate turns of the spirallywound electrode or between the last outer turn and the container wallwhich does not interfere with the free circulation of the electrolyticliquid, I have found a porous, i. e. loosely woven fabric best suited.iThe material may be linen, silk, cotton or the like and the preferredform in which said material is made, is coarse gauze, offering the leasttotal resistance and yet enough stiffness, not to collapse when wet. Thelatter quality can be improved and lightened by impregnating the gauzewith a medium which not only Waterproofs it but also protects'the fiberagainst the attack of whatever electrolyte may be used. Common glue orstarch with which the commercial grade of gauze is sometimesimpregnated, dissolves in borax solution-which is the most commonly usedelectrolyteand other electrolytes like sulphuric acid which sometimes isused-especially when the anode is made of tantalum instead ofaluminum-would attack the fiber itself. Rubberizing the gauze, however,or impregnating it with a suitable lacquer, i. e. with celluloiddissolved in acetone or amyl-acetate will make it waterproof, as well asresistive to practically any of the well-known electrolytes, at the sametime increasing its stiffness and dielectric strength without impairingits porosity.

The insulating gauze 48 may be combined with the metallic spiral 22 intwo different ways. It may start with and be fixedly attached to thelatter at the inner edge of the spirally wound sheet, which is creasedat a sharp angle at 41 all the way up to the top of the anode element,as indicated in Fig. 2. In this way it covers the total area of themetal sheet and inaddition it protrudes at the outer end, at A, so farthat it can be wound around the outside of the spiral roll for more thana whole turn to insulate it against the container wall. Furthermore, thegauze should be of somewhat greater width than the aluminum sheet so asto guard the edges of the spiral roll against any short circuit bysparking over from the cathode or by accidental contact of the innerturns with each other, while the water level, of the electrolytesolution should be kept even higher than the top rim of the gauze.

Considering the natural tendency of any spiral spring which is fastenedat the inner end and confined within a circular or cylindrical space, toexpand its turns the more they get away from the center which widens thespacing between the inner turns and narrows it between the outer turns,it will be found superfluous to insulate the turns of smaller diameterfrom each other and it will be found suflicient if the insulating gauzeis inserted between the outer turns only. as indicated in Fig. 3. Theinsulation between the last anode spiral turn and the container,however, should preferredly consist of a double layer of insulatinggauze as shown in the same view.

As Figures 7 and 8 illustrate, means may be provided to secure the upperends of the insulating sheets and the corners of the anode spiralrespectively in place. At A the extreme outer corner of the aluminumsheet is creased over by what is usually called a dogs ear, as at 50,Fig. 7. This is passed through a slot in the gauze and clipped over soas to clamp the gauze tightly to the metal. Fig. 8 shows a modificationadapted to clamp the end of the gauze sheet to the edge of the aluminumsheet, which continues, as is the case at point B, Fig. 3. A smallrectangular incision is made in the edge of the metal sheet so that alittle square clip can be bent sideways and creased over the edge of thegauze, clamping the two sheets securely together.

Finally the whole spiral roll, comprising the aluminum sheet and theinsulating gauze may be bound together by two annular bands 21,

preferredly'of soft rubber.

It will be evident that the fine gas bubbles which originate due toelectrolytic action, are liable to get enmeshed and arrested by thenetting of the gauze whereby they lose at least a part of their electriccharge before they coagulate into bigger bubbles which will floatupwardly. At the same time the gauze netting will provide an eflicientarrester of gas bubbles coming from the anode and attracted by theopposite polarity of the cathode wall.

It is obvious from the described construction that not only thefilm-forming on the cathode, due to the causes explained, is effectivelyobviated but also the other objects listed are obtained.

In accordance with the provisions of the patent statute, I havedescribed my invention, but I desire it understood that it is notconfined to the particular form shown and described, the

same being merely illustrative, and that the' invention may be carriedout in other ways without departing from the spirit of my invention, andtherefore I claim broadly the right to employ all equivalentinstrumentalities coming within the scope of the appended claims, and bymeans of which; objects of my invention are attained and new resultsaccomplished, as it is obvious that the particular embodiments hereinshown and described are only some of many that can be employed to attainthese objects and accomplish these results.

Having now described my invention, what I claim as new, and desire tosecure by Letters Patent, is:

1, In an electrolytic condenser, the combination with a container for aliquid electrolyte and adapted to serve as cathode electrode and aloosely wound film-forming metal sheet, insulatingly supported withinsaid container and serving as anode electrode; of a wide meshednonconducting fabric sheet, inter-leaved between the spiral turns of theanode sheet and also between the last outer turn and the inside of thecathode-forming container, said fabric sheet being of such a width as toexceed the width of the anode zheet, measured parallel to the spiralaxis.

2. In a condenser employing a liquid electrolyte comprising aspiral-wound film-forming anode and a metallic container serving ascathode,

means to intercept the gas bubbles generated by the electrolytic actionand to neutralize their electrical charge by mechanical contact, saidmeans comprising a wide meshed fabric sheet, interleaved between theouter turn of the spiral anode and the metallic container.

3. In a condenser employing a liquid electrolyte,

aluminum container serving as cathode, means to intercept the gasbubbles generated by electrolytic action near the anode and to preventthem from forming a film on the cathode, said means comprising anon-conducting gauze mantle, surrounding said aluminum anode, said gauzeimpregnated with an agent insoluble in the electrolyte.

5. In a condenser, employing a liquid electrolyte and comprising analuminum anode and an aluminum container serving as cathode, means tointercept the gas bubbles generated by electrolytic action near theanode and to prevent them from forming'a film on the cathode, said meanscomprising a non-conducting gauzemantle, surrounding said aluminumanode, and means to fixedly suspend said gauze mantle from the aluminumanode.

6. In an electrolytic condenser, comprising a spiral-wound anode,consisting of a perforated aluminum sheet and an aluminum container fora liquid electrolyte serving as cathode, means to insulate the anodefrom the cathode and to prevent gas bubbles generated by electrolyticaction at the anode from forming a film on the cathode, said meanscomprising a non-conducting gauze mantle, interposed between the spiralroll of the anode and the cathode container.

7. In an electrolytic condenser, comprising a spiral-wound anode,consisting of aluminum and an aluminum container for a liquidelectrolyte, serving as cathode, means to intercept the gas bubblesgenerated by electrolytic action and to neutralize their charge bymechanical contact, saidmeans comprising a non-conducting gauze sheet,superimposed upon the spirally wound anode, interleaved between theseparate turns and surrounding the last turn, so as to securely insulatethe anode from the cathode container.

-8. An electrolytic condenser consisting of an outer metallic container,serving as cathode and a film-forming anode, insulatingly suspended in aliquid electrolyte within the container, said condenser adapted topermit free circulation of the electrolyte upwardly through the middleand downwardly at the inner wall of the container with a free radialpassage between these two courses, and comprising a perforated anodesheet, loosely folded together to substantially occupy the space withinthe container, leaving a free central space, and an insulating gauzefabric, suspended between the folds of the anodesheet, and also betweenthe latter and the inside of the container.

JOSEPH A. POITRAS.

